In the process for converting iron to steel using the oxygen blowing technique, an overhead water-cooled lance is used to force purified oxygen under high pressure against the surface of the molten metal in a refractory lined, closed bottom converter. While the oxygen lance is inserted within the converter, a sensor lance may also be lowered into and retracted from the converter during the operation to test the melt. Usually these metallurgical lances extend through the hood of a vent or duct system which covers the mouth of the converter to collect for cleaning and scrubbing the hot gases which are generated during the blowing process.
By ejecting the oxygen from the end of the lance at very high velocities, the oxygen impacts the surface of the molten metal which is covered by a layer of slag such that the slag and other molten materials are splashed about within the converter. Some of this molten material contacts the relatively cool outer surface of the metallurgical lances and solidifies there forming what is commonly called a skull. If not removed, the solidified material can quickly accumulate on the lances to the point where the added weight and the increased dimension of the skull-containing lance interfere with efficient operation. The coating may become so thick that the lance cannot be withdrawn from the opening in the hood or so heavy the hoisting means cannot lift the lance. Moveover, if the skulls are not removed from sensor lances after each test, they interfere with the injection of test devices in subsequent tests. This leads to operating downtime to remove the skulls by prying with a bar or cutting with a torch.
An appreciation of the problem created by the presence of skulls on metallurgical lances can be gained from a review of the methods and apparatus which have been devised in attempts to solve this problem. In U.S. Pat. No. 3,394,928 a device is disclosed for clamping a lance, which device holds the lance with sufficient pressure to prevent excessive vibration during blowing and also descales the lance as it is retracted. U.S. Pat. No. 3,575,706 discloses that skull buildup on the lance can be materially reduced or prevented by applying to the lance a coating of an oleaginous composition containing finely divided inorganic particulate matter. A cleaning device is described in U.S. Pat. No. 3,907,264 that comprises a scraping means to contact and scrape the outer surface of the lance as it is raised from the converter to automatically remove adhered material. In U.S. Pat. No. 3,912,244 an oxygen lance is disclosed that has a water spray system incorporated into the structure of the lance including exit water spray nozzles in the wall of the lance barrel for emitting a water spray from the water jacket around the barrel to prevent skull formation. Another method and apparatus for removing encrustations from a metallurgical lance is disclosed in U.S. Pat. No. 4,052,044. A tool is displaced relative to the lance and in contact with the layer of encrustation on the lance. A repetitive movement is applied to the tool against the layer to dislodge it. Some of the prior art devices while attempting to remove a tenaciously adhering skull may gouge the lance or impart such an opposing force that the hoisting mechanism is overstressed.
Consequently, there still exists a need for a reliable apparatus that quickly and efficiently removes a skull from a metallurgical lance.
There is a further need for a deskulling device that prevents digging and gouging on the surface of the lance.
There is yet a further need for an apparatus that does not overstress the lance hoisting system when the skull is welded to the lance and cannot be readily removed.